Building of underground pipelines can be done according to several different principals. The most simple way is to dig ground away in the place where the pipeline is planned to be and to lay down pipes in the excavation and refill the excavation. However this can not always be done with open excavation, for instance because of roads or lakes. In these cases one must use some kind of underground method.
In case of small diameter pipes and short distances, soil displacing methods can be used in which the pipe is pressed in the desired direction by a force strong enough to move the pipe. In the end of the pipe there is placed a formed point which displaces the soil as much as the pipe requires. An apparatus based on such displacement of soil is presented in patent document FI-51726. While it is relatively easy to make small holes by this method, in case of larger diameter holes, friction against displacement becomes so strong that energy sources available to be used in this purpose, can not produce the force needed, or use of them is uneconomical. Because of this, in case of larger diameter holes, one has to use mechanical hammers or cutters.
In production of larger diameter holes, loosened soil must be removed from the hole. For instance in patent document FI-51726 there is shown a method to remove broken soil from the hole through the pipe by pressurized air.
In other earlier known method for removal of loosened soil is for instance a transportation screw assembled in the pipe following the drill head, as is shown for instance in German patent document DE 33 06 047. In the system described in this document, a drill head is assembled in the supporting pipe which contains a transportation screw. The diameter of this screw is such that its outer diameter is nearly equal to inner diameter of supporting pipe. In this construction, the transportation screw is moving in relation to supporting pipe.
In German patent document DE 32 28 684 there is shown a construction in which the transportation screw is located in the supporting pipe whose diameter is essentially smaller than diameter of the pipe to be assembled. In this case, location or direction determination of drill head can be executed through an upper area of the pipe, which is remaining free.
As defects of present methods one can mention that visual observation of drill head is limited. Also, reparation requires a drawing out of the drill head, which operation in many cases is difficult and takes a long time.
Also as a defect can be mentioned that the construction of the transportation screw limits the diameter of rocks able to be transported through the screw. Also, emptying of a clogged transportation screw is difficult, because construction of the screw is closed.